Microfibrillated plant fibers such as cellulose fibers can be incorporated as filler in a rubber composition to reinforce the rubber composition and enhance the modulus (complex modulus). However, microfibrillated plant fibers have strong self-aggregation properties and poor compatibility with the rubber component. For this reason, for example, when microfibrillated plant fibers are added to rubber latex and then mixed, unfortunately approximately 20% of the added microfibrillated plant fibers cannot be incorporated into the rubber component and still remain in the solution.
In the case where rubber latex is mixed with microfibrillated plant fibers to prepare a masterbatch, agglomerates of the microfibrillated plant fibers are likely to be formed in the masterbatch. For this reason, if this masterbatch is used for a tire, the formed agglomerates may cause premature wear, cracks, chipping, and interlayer separation. Further, the agglomerates may even cause leakage of air and loss of handling stability.
As mentioned above, there is room for improvement in that, though improving the modulus, the addition of microfibrillated plant fibers may reduce the required performance for a tire, that is, handling stability, abrasion resistance, and durability, and therefore eliminate the functional merit of the tire.
Patent Literature 1 discloses a method for improving the compatibility between the rubber component and microfibrillated plant fibers by a chemical modification of the microfibrillated plant fibers. However, this method is also not sufficient for overall improvement in the above performance properties.